Cable television (CATV) networks have evolved significantly since first being deployed as systems that delivered video channels one-way from a content provider. These early systems included transmitters that assigned a number of CATV channels among several frequency bands, each of approximately 6 MHz, multiplexed those signals, and sent them to subscribers as an electrical signal through a network of coaxial transmission lines to cable modems or set-top boxes in subscribers premises. Early evolution of such systems permitted limited return communication from the subscribers back to the content provider either through telephone lines or a dedicated, small, low-frequency signal propagated onto the coaxial network.
As the cable television infrastructure evolves, the upper boundary of the upstream band (e.g., return band) frequency in a CATV system may be extended by increasing the frequency of the split between the upstream band (e.g., upstream channel) and the downstream band (e.g., forward band); this allocates more bandwidth to the upstream band. The upstream band is dedicated to the transport of signals from customer premise equipment (e.g., set-top boxes or other components) to the CATV head end, and the downstream band is dedicated to the transport of signals from the CATV head end to the customer premise equipment. Extending the upstream band will enable more upstream bandwidth capacity due to the increased upstream spectrum. However, reallocating spectrum to the upstream consumes a portion of the spectrum previously dedicated to the downstream band. Thus, increasing the upper boundary of the upstream band frequency may interfere with CATV components that still communicate or require downstream communication signals that fall within the frequency reallocated to the upstream band.
When multiple service operators (MSOs) start providing higher-speed services using a higher-split architecture, such as a mid-split or high-split architecture, the upstream signals from customer premise equipment may interfere with other, older legacy devices that still receive downstream signals within the same frequency spectrum. For example, using a mid-split architecture where customer premise equipment in the subscriber's premises transmits upstream within the 5-85 MHz upstream spectrum, legacy devices still receive downstream signals within the 54-85 MHz band. The customer premise equipment that transmits upstream in the 54-85 MHz band may cause issues with the older legacy devices.